1. Field of Invention
This invention relates to dental restorations, specifically to the contouring of restorative material utilizing matrices and burnishable.
2. Description of Prior Art
Dental matrices of the art are flat, flexible strips of material which may be contoured into shapes which resemble surfaces of teeth. Matrix strips are manipulated to approximate the desired shape of the restoration. The strips provide a contourable surface, whereby hardenable restorative materials may be partially contained and manipulated into desirable contours prior to hardening. Matrices of the art are comprised of flat strips of thin steel, flat strips of mylar, or other similar materials.
The metal strips have a thickness ranging from 0.001 to 0.002 inches. Metal matrices are used more often for restoring posterior teeth, as they are less likely to tear than transparent strips.
Transparent strips are primarily used as matrix strips for esthetic restorations. Theses are typically comprised of 0.002 inch thick acetate, known as Mylar (3M). The transparency provides access for the curing light, as the strip frequently covers the restoration.
Metal and Mylar strips of less thickness than those cited tend to wrinkle or tear, such as when fitting through interproximal contact areas between teeth. It is not practical for a dentist to reduce the thickness of mylar or metal strips, such as by burnishing.
Metal and transparent strips are typically flat, and relatively stiff, and exhibit substantial memory for their shapes. As a result, they readily cut the interproximal gingival papilla, and initiate bleeding. Bleeding is a major impediment for restoration bond strengths and esthetics. Matrix memory also tends to interfere with the operator's efforts to mold the restorative material to physiological contours. As such, restorations formed with matrices of the art tend to be molded somewhat nonphysiologically. This creates any of several problems, including overhangs, food traps, plaque and stain traps, open contacts, ledges, shredding dental floss, open embrasures, poor esthetics, chronic gingival inflammation, voids, and so on.
Further, matrices of the art must be forcefully retained against the critical gingival margin of a tooth cavity preparation as uniformly as is possible. Otherwise the matrix tends to pull away from the restorative material, and the margins. This requires a matrix retainer device, or a continuous operator finger pressure. Such retaining of matrices of the art interferes with the ease of molding restorative materials.
A wedge is used to conform matrix strips of the art, as much as possible, to the shape of the gingival margins of the preparation. However, portions of the strip tend to remain a distance from the preparation margins. This permits the restorative material to form undesirable overhangs along the preparation margins.
Wedges are used simultaneously to temporarily, slightly separate the teeth, to compensate for the thickness of the strip. Steel and Mylar matrices do not readily burnish to a reduced thickness. After the restoration is hardened, the strip is removed, and the teeth move back together. As such, the adjacent tooth is able to maintain proper contact with the restorative material. However, wedges tend to traumatize the interdental papillae, and promote bleeding.
Composites are hardenable restorative materials which contain adhesive resins. The curing, or hardening, of such resins is substantially inhibited in the presence of oxygen. An uncured oxygen inhibited resin layer, which forms at the exposed outer surface, facilitates strong bonding to subsequent additions of restorative material. Matrix strips of the art are nonporous, and thus shield the composite from oxygen. As such, they eliminate the oxygen inhibited layer. Further additions of unhardened restorative material to hardened, noninhibited surface material results in substantially weakened bond strengths.
In addition to contouring restorative materials, matrixes of the art also act as separators. Separators can be defined as any material or device which provides a barrier surface to prevent contact between substances. Separators include paints, gels, and strips of various materials. Howard Stean, in "PTFE Tape: A Versatile Material in Restorative Dentistry", DENTAL UPDATE, Vol. 20, No. 4, May 1993, discloses utilizing a soft polymer strip, PTFE (DuPONT Teflon.RTM. polytetrafluoroethylene), tape as a separator. Dr. Stean specifies utilizing the PTFE tape as a barrier to prevent inadvertent adhesion of luting cement with adjacent teeth, when cementing porcelain veneers. The PTFE tape is preferred as a separator because it can be burnished thin, to prevent displacement of porcelain veneers during cementation. In contrast, the thickness of the metal and mylar strips, as separators, would displace veneers from proper positioning on the teeth. As a result, the cleanup of hardened cement was made easier, without compromising the positioning of the veneers.
However, such use of PTFE tape for cementation of porcelain veneers never achieved widespread use for a variety of reasons. The thread seal tape commonly available in plumbing stores is fragile and difficult to use. Further, the process does not specify a technique for inserting the tape between interproximally contacting tooth preparations. Still further, current cementation technique prefers partly hardening the cement without any separator, followed by cleaning the excess cement, and completely hardening the remaining luting cement.
The above matrix strips suffer from a number of disadvantages:
(a) Matrix strip processes specify concurrent use of a wedge to mold a restoration to contact the adjacent tooth. PA1 (b) Matrix strips are not readily burnishable to insubstantial thickness. PA1 (c) The substantial shape memory of matrix strips tends to interfere with shaping unhardened restorative material. PA1 (d) Matrix strips require applied tension to retain their position. PA1 (e) Matrix strips tend to form overhanging restoration margins. PA1 (f) Matrix strips substantially eliminate the oxygen inhibited layer of composite restorative materials. PA1 (g) Matrix strips tend to cut the gingiva when placed to cover gingival margins. PA1 (h) Matrix strips do not absorb bonding resins. PA1 (i) No matrix strip process substantially blocks out all surface undercuts available to restorative material molded in a prepared tooth, and molded against substantially unshimmed interproximal contact areas. PA1 (j) No matrix strip process provides a separating layer between surfaces of a prepared tooth and permanent restorative material against substantially unshimmed interproximal contact areas. PA1 (k) No matrix strip process provides for molding restorative material in a prepared tooth, against substantially unshimmed interproximal contact areas, without unseating during a pliability stage, then hardened, and removed from the tooth, without substantial deformation, fracture, or abrading of the restorative material. PA1 (l) No matrix strip process provides for molding restorative material by impression imprint in a prepared tooth, against substantially unshimmed interproximal contact areas, then hardened, and removed from the tooth, without substantial deformation, fracture, or abrasion. PA1 (m) Processes utilizing matrix strips to form removable permanent restorations specify the use of separators which create separation spaces which are inconsistently too wide or too narrow. PA1 (a) to provide a matrix strip which permits the restorative material to contact the adjacent tooth without requiring the use of a wedge; PA1 (b) to provide a matrix strip which is readily burnishable to insubstantial thickness; PA1 (c) to provide a matrix strip which is dead soft, so that it adapts readily to the desired shape of the restoration, yet stabilizes the shape of the moldable restorative material; PA1 (d) to provide a matrix strip which does not require applied tension to be retained in position; PA1 (e) to provide a matrix strip which facilitates molding restoration margins without overhangs; PA1 (f) to provide a matrix strip which substantially preserves the oxygen inhibited layer of composite restorative materials; PA1 (g) to provide a matrix strip which does not tend to cut the gingiva when placed to cover gingival margins; PA1 (h) to provide a matrix strip which absorbs bonding resins; PA1 (i) to provide a matrix strip which is readily burnishable to insignificant thickness over the interproximal contact area, and separates restorative material from prepared tooth surfaces, such that the restoration is removable from the prepared tooth; PA1 (j) to provide a matrix strip process that substantially blocks out all surface undercuts available to restorative material molded in a prepared tooth, and molded against substantially unshimmed interproximal contact areas; PA1 (k) to provide a matrix strip process that specifies a separating layer between surfaces of a prepared tooth and permanent restorative material molded against substantially unshimmed interproximal contact areas; PA1 (l) to provide a matrix strip process that specifies molding of restorative material in a prepared tooth, and against substantially unshimmed interproximal contact areas, without removal during a pliability stage, partial hardening of the restorative material, and removal of the hardened restorative material from the teeth without substantial deformation, fracture, or abrasion of such material; PA1 (m) to provide a matrix strip process that permits impression imprint molding of unhardened restorative material in a prepared tooth, against substantially unshimmed interproximal contact areas, partial hardening of the restorative material, and then removal of the hardened restorative material without substantial deformation, fracture, or abrading of such material; PA1 (n) to provide a process utilizing matrix strips to form removable permanent restorations that specifies the use of separators which create separation spaces which are consistently adequate; PA1 (o) to provide a matrix strip process that specifies an interproximal contouring matrix for restorative materials, but leaves interproximal contact areas substantially unshimmed, such that a wedge is not needed; PA1 (p) to provide a matrix strip which has an affinity for dental resins, and resin restorative materials.
A device similar to my matrix strip is not obvious because it is not readily apparent that a soft matrix strip can enhance contouring of restorative materials, especially without wedging, facilitate the formation of flush restoration margins, or be readily inserted into tightly contacting interproximal spaces. Neither is it apparent that a matrix strip can preserve the oxygen-inhibited layer of composite restorative materials, or that a semi-opaque matrix permits sufficient curing of light catalyzed restorative materials. Neither is it apparent that a soft polymer strip can permit accurate formation and removal of hardenable restorative material from a prepared tooth, or that stabilizing a soft polymer strip to dental surfaces is a valuable adjunct to dental processes.